text: In two-stage process, reaction and oxidation are carried out separately in tubular reactors. Unlike one-stage process, air can be used instead of oxygen. Ethylene is passed through the reactor along with catalyst at 105–110 °C and 900–1000 kPa. Catalyst solution containing acetaldehyde is separated by flash distillation. The catalyst is oxidized in the oxidation reactor at 1000 kPa using air as oxidizing medium. Oxidized catalyst solution is separated and sent back to reactor. Oxygen from air is used up completely and the exhaust air is circulated as inert gas. Acetaldehyde – water vapor mixture is preconcentrated  to 60–90% acetaldehyde by utilizing the heat of reaction and the discharged water is returned to the flash tower to maintain catalyst concentration. A two-stage distillation of the crude acetaldehyde follows. In the first stage, low-boiling substances, such as chloromethane, chloroethane and carbon dioxide, are separated. In the second stage, water and higher-boiling by-products, such as chlorinated acetaldehydes and acetic acid, are removed and acetaldehyde is obtained in pure form overhead.
  Due to corrosive nature of the catalyst, the equipments in contact with it are lined with titanium.
  In both one- and two-stage processes the acetaldehyde yield is about 95% and the production costs are virtually the same. The advantage of using dilute gases in the two-stage method is balanced by higher investment costs. Both methods yield chlorinated hydrocarbons, chlorinated acetaldehydes, and acetic acid as byproducts. Generally, the choice of method is governed by the raw material and energy situations as well as by the availability of oxygen at a reasonable price.
  In general, 100 parts of ethene gives:
  * 95 parts acetaldehyde
  * 1.9 parts chlorinated aldehydes
  * 1.1 parts unconverted ethene
  * 0.8 parts carbon dioxide
  * 0.7 parts acetic acid
  * 0.1 parts chloromethane
  * 0.1 parts ethyl chloride
  * 0.3 parts ethane, methane, crotonaldehyde
  and other minor side products